The thing about Royal Gorge is, nobody really knows how big it is. Trail reports have varied since the cross-country ski resort went up on Donner Summit in 1971, suggesting the nearly 3,000-acre property offers anywhere between 195 to 320 kilometers of groomed terrain. Back in the early stages of the Royal Gorge’s rapid development in Soda Springs, Calif., founder John Slouber claimed it was the largest nordic ski area in North America. Forty years...